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Ask Dr. Dave

August 1, 2006
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August 2006

Question: We need some seals and gaskets for handling caustic solutions in our plant. What would you recommend?

Answer: Several elastomers have been used for this type of application, including EPDM and hydrogenated nitrile (HNBR). However, the elastomers that are most recognized for aggressive environments like this are the so-called FKMs. The abbreviation "FKM" is the ASTM designation for fluoroelastomers or fluorine-containing rubbers. FKMs have traditionally been one of the most chemically resistant polymers for sealing applications. Since these rubbers have to be heat-cured to develop optimum properties, you would normally buy the solid seals and gaskets from your seals distributor. However, while all FKM seals will have some base resistance, for maximum longevity the rubber in your seals should be compounded from special forms of fluoroelastomers that usually have the letters BR (base-resistant) before the number designation. Your seal supplier should be familiar with these. Some companies are now offering two-component adhesives and sealants based on fluoroelastomers that you can mix and cure at room temperatures or elevated temperatures. Another type of fluoroelastomer that is also recommended for this application is commonly called TFEP (which stands for tetrafluoroethylene/propylene copolymer). The best bets in sealing performance are probably encapsulated seals and gaskets where an elastomer core is encapsulated with PTFE, although these tend to be extremely expensive. You will have to test some of these products to determine the longevity of the seals in your plant and the cost effectiveness of the different technologies.

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